The present invention relates to an antireflection film for a window of a transport, a glass provided with an antireflection film for a window of a transport, a laminated glass provided with an antireflection film for a window of a transport and its production process. Particularly, it relates to a light absorptive antireflection film which reduces reflection of oblique incident light, a glass for an automobile using said antireflection film, a laminated glass for an automobile and its production process.
Conventionally, since the reflectance of visible light (hereinafter referred to simply as reflectance) from the film face side (interior side) of a windshield of an automobile is high, the color tone of e.g. the interior has been limited to one based on dark tone color (such as black), in order to suppress reflection of the dashboard and its surrounding, and to increase visibility of the driver. That has significantly restricted, the color of the car interior, and significantly limited the design of an automobile.
In recent years, the setting angle of a windshield tends to be acute, from the viewpoint of the appearance design, and accordingly, the problem of the reflection on the interior face tends to be more significant.
Accordingly, it has been required to reduce the reflectance on the interior face of a windshield and to increase the allowable range of the interior design.
As a method to achieve such requirements, it has been known to form an antireflection (hereinafter sometimes referred to simply as AR) film on the surface of a windshield. For example, the following methods such as 1) a method of forming a transparent multi-layer AR film, and 2) a method of forming a transparent single-layer AR film, have been proposed.
The method 1) is to form a known multi-layer AR film by vacuum deposition or sputtering. However, since the total film thickness is so thick as at least about 250 nm, the cost required for the production is high, and further, coating is required on both inside and outside the car to obtain an adequate AR function, such being problematic. Further, since the outside of the car is always abraded by wipers, an extremely high abrasion resistance is required, but the abrasion resistance is inadequate with conventionally known film materials.
In the method 2), in the case of the vacuum deposition, MgF2 may be coated. However, it is necessary to form a film on a hot substrate in order to let MgF2 have an adequate strength, and stability of the film thickness distribution which is characteristic of the deposition is inadequate, such being problematic in productivity. Further, the problem of the abrasion resistance on the outside of the car is similar to the case of the method 1). In recent years, a single-layer AR film having a high strength has been developed by using porous SiO2 (porous silicon oxide). However, the abrasion resistance on the outside of the car is inadequate, and dirt attached to the pores during long-term use is less likely to be removed.
On the other hand, as a low-reflection film for CRT, a new type multi-layer AR film comprising a light absorbing film as a constituent has been proposed (JP-A-64-70701, U.S. Pat. No. 5,091,244). With this multi-layer AR film, the visible reflectance on the surface can be made 0.3% or less, the sheet resistance of the surface can be made 1 kxcexa9/xe2x96xa1 or less, and further, the electromagnetic wave-shielding effect can be imparted. Further, since a light absorbing film is used, the entire transmittance of visible light (hereinafter sometimes referred to simply as transmittance) will decrease, whereby the contrast can be increased. However, if this multi-layer AR film for CRT is directly applied to a windshield for an automobile, the desired effect can rarely be obtained. Namely, as mentioned above, a windshield for an automobile is set in a significantly slanted state, and accordingly, with the film constitution for CRT which is designed for incident light at right angles, no adequate AR performance will be obtained, or the reflection color tone tends to be yellowish or reddish, such being problematic.
Further, a windshield for an automobile is required to shield the direct solar radiation light as much as possible from the viewpoint of the temperature in the car, and a green type heat absorbing glass is mainly used at present. This glass slightly reduces transmittance at the visible light region. Accordingly, also in the case of using the above AR film comprising a light absorbing film, it is preferred to make the transmittance as high as possible and to use it together with a heat absorbing glass.
However, with respect to a conventionally known absorptive type AR film for CRT, the transmittance is considered to be preferably low in order to improve the contrast, which is one reason to make it difficult to apply the film to a windshield for an automobile.
As another example of the AR film for CRT, a four layer constitution of glass/transition metal nitride/transparent film/transition metal nitride/transparent film, has been known (U.S. Pat. No. 5,091,244). However, this multi-layer AR film is designed to have a transmittance of visible light of 50% or less, and further, the absorbing layer is divided into two layers to make the number of layers at least four layers to achieve this, and thus many steps are required.
Production of a windshield for an automobile most advantageously comprises coating on a flat glass substrate, followed by cutting, bending and lamination. However, although it is described that the conventional AR film for CRT may resist heat treatment after coated on a panel glass (such as heat treatment in the frit seal step) (JP-A-9-156964), the temperature for the heat treatment is a level of 450xc2x0 C., and no result of studies has been shown with respect to a high temperature of from 560 to 700xc2x0 C. in the step of bending in production of a windshield for an automobile.
The present invention has been made to overcome the above-described drawbacks of the prior art and to provide an antireflection film for a window of a transport, having an adequately low reflection performance to oblique incident light (particularly oblique incident light at an angle of a level of 60xc2x0), an adequate abrasion resistance and a high transmittance of visible light, and a glass provided with an antireflection film for a window of a transport comprising said antireflection film (particularly a glass for an automobile provided with an antireflection film and a laminated glass for an automobile provided with an antireflection film).
The present invention further provides an antireflection film for a window of a transport which presents neutral reflection color tone (color tone close to colorless) to oblique incident light (particularly oblique incident light at an angle of a level of 60xc2x0) and a glass provided with an antireflection film for a window of a transport comprising said antireflection film (particularly a glass for an automobile provided with an antireflection film and a laminated glass for an automobile provided with an antireflection film).
Further, it is an object of the present invention to provide an antireflection film for a window of a transport which adequately resists heat treatment (such as heat treatment in the bending step or the tempering step) in production of a glass for an automobile and which is excellent in productivity at a low cost, and a glass provided with an antireflection film for a window of a transport comprising said antireflection film (particularly a glass for an automobile provided with an antireflection film).
Further, it is an object of the present invention to provide a laminated glass provided with an antireflection film for a window of a transport, comprising the above antireflection film (particularly a laminated glass for an automobile provided with an antireflection film), and a production process to easily obtain a laminated glass provided with an antireflection film for a window of a transport.
The present invention has been made to overcome the above-described problems, and provides an antireflection film for a window of a transport, which comprises a light absorbing film consisting essentially of a nitride and an oxide film having a refractive index of from 1.45 to 1.70 formed on a substrate in this order on the substrate, wherein the geometrical film thickness of the light absorbing film is from 3 to 12 nm, and the geometrical film thickness of the oxide film is from 70 to 140 nm (a first invention).